Coloration of aluminum articles



a coloration of aluminum Patented Oct. 29, 1935 UNITED STATES PATENToer-ice 2,019,229 4 COLORATION 0F ALUMINUM ARTICLES James Francis Leahy,

to Atlas Tack Corpor- Fairhaven, Mass., assignor ation, Fairhaven,Mass., at

No Drawing. Application November 16, 1931,

Serial No.

5 Claims.

The subject of this invention is the coloration of aluminum objects andmore particularly small aluminum articles, such the like. It has been asbuttons, eyelets and found possible to efiect by using the aluminum baseitself as a component entering into the chemical formation of thecoloring material. More specifically it has been found that thesuperficial oxidation of aluminum articles to produce surface films orcoatings of aluminum oxide on such articles, followed by the treatmentof the articles with lake-forming dyes, results in the generation ofinsoluble color lakes tenaciously adherent to the aluminum base, thereaction evidently being analogous to that occurring when mordant dyesare fixed on textile goods with mordants of the class of aluminum oxide.

I have now discovered that if the oxide film formed on aluminum articlesis brought to a predetermined condition of hydrogen ion concentration,more especially on the alkaline side of neutrality, it is possible tocontrol and extend the tones of color or color effects and theappearance developed on the articles with the available lake-formingdyes.

I have further found that by imparting a predetermined alkalinity to thealuminum oxide film, it is possible to ensure smooth and positivereaction between the film and the lake-forming dye to p roduce delicateand iridescent color lakes characterized by tenacious adherence to themetal base.

effect obtained in any particular upon the pH value or alkalini Thecolor case depends y of the solution to which the oxide film is exposed,and upon such other factors as ment with the alkaline reagents.

While there are various ways 0 time and temperature of treatfsuperficially oxidizing aluminum articles, I prefer to bring about suchoxidation disclosed in my application 452,525, filed May 14, 1930.

articles precisely as by a treatment such as Serial Number I shalltherefore now give a specific example of procedure involving an initialoxidizing. treatment of aluminum described in that application.

Aluminum articles, such as buttons, are placed in a suitable perforatedcontaine r of basket, and

the basket then immersed in a solution of about 2% sodium carbonate andabout /z% sodium bichromate, preferably at boiling temperature, as

o accelerate the oxelevated temperature serves t idizing reaction.

The articles need remain in contact with the boiling solution for onlyfive to fifteen minutes, coating or skin of at the end of which time aoxide of the desired depth has been produced and little further reactiontakes place, probably owing to the impermeable character of the coating.then removed from the The The basket of articles is solution and may bewashed free of entrained solution,

as by dipping oxide coating formed on the articles is a mixture of bothaluminum and chromium oxides, the sodium bichromate evidently beingreduced by the metallic aluminum into an oxide while serving to oxidizethe metallic aluminum into an oxide. The coating has a'gray colorcharacteristic of a mixture of both the aluminum and chromium oxides.

In accordance with the present invention, the batch of articles is thenimmersed in a solution of predetermined alkalinity, for instance, in asolution of both sodium carbonate and sodium tetraborate of about onetenth normality and in which the ratio of sodium carbonate to sodiumtetraborate is about nine to one. The articles may be kept below thesolution at about room temperature for about five minutes. The batch ofarticles may then be removed from the solution and subjected to thefinal dyeing operation. The alkaline treatment visibly modifies theoxide 20 film, changing it from an opaque, dull-gray color to acondition of translucency or transparency. The thickness of the film isalso reduced owing -to the removal of considerable, if not all, of thechromium oxide as well as some of the aluminum 25 oxide.

The dyeing of the articles may be performed in various lake-forming dyesolutions. For instance, the batch of articles may be lowered into abath of dye solution at about boiling temperature containing, forinstance, 1% alizarin dye of the desired color, say, red, blue, green ora mixture of colors. The dye bath preferably contains about 1% of aweakly ionized acid such as formic, acetic, lactic, tartaric, boric orphosphoric; and the articles are permitted to remain in'contact with thedye solution for about 15 minutes, at the end of which time practicallyequilibrium coloration has been efiected. When alizarin sapphire is thedye employed the articles acquire an iridescent blue coloration,whereas, when alizarin orange is the dye employed, a delicate,gold-colored lake is fixed on the articles. Theuse of a dye bath atelevated temperature is highly desirable in that the reaction to formthe colored coating or color lake is greatly accelerated by increase oftemperature, comparatively little reaction taking place at roomtemperature. The colored articles may then be dried; and, if desired,this may be effected 50 in a current of warm air, particularly inasmuchas no visible discoloration takes place under such conditions. The colorlake formed on the article is resistant to scratching or abrasion and ischaracterized by its tenacity. It is firimly bonded with the aluminumbase, although it can be removed by a hard, sharp instrument. The colorlake also resists removal even by repeated treatment in solutions ofalkali or soap, such as are used for laundering a0 density, hardness and55,

The alkaline solution hereinbefore described for modifying the oxidefilm is subject to consid erable variation in composition, dependingupon the final color effect to be produced. Thus, the

at about one-tenth normality, so that flexibility or control of thereaction on the film may be had.

It is highly likely that under the conditions given in the citedexample, the chromium oxide content or the film is pracof relatively lowalkalinity, may serve to cause the desired modification oi the oxidefilm. This modification is, as already indicated, accomdesired end-pointof treatment.

I have adverted to the washing or rinsing oi the preliminarily oxidizedarticles before they undergo the second The articles may, however,

in wash water, and finally in the dye bath. It is desirable, however, tomaintain the oxide film in a wet or freshly i'ormed state throughout theprocess, since when the oxide film is once dried out, it does not reactas desired with the dye solution unless it is rehydrated by ored to thedesired shade and that spoilage losses It is to be observed thatalthough the initial treating solution may be slightly alka- 1 What Iclaim is: 1. A process which comprises treating aluminum articles witha. solution of an oxidizing agent to form a coating of aluminum oxidethereon,

on such articles.

2. A process of coloring small aluminum arti- 30 cles which comprisessubjecting a batch of such articles to a succession of treatments,including ,10 and 11, and finally a treatment with a lakeforming dyesolution to generate an insoluble color lake on such articles.

3. A process of coloring small aluminum articles which comprisessubjecting a batch of such articles to a succession between about 10 and11, ment with a lake-forming dye solution to generate an insoluble lakeon such articles.

4. A process of coloring aluminum articles 11, and finally treating thearticles with a lake-forming dye to generate an insoluble 70 color lakeon such articles.

JAMES FRANCIS LEAHY.

